Conventional toothbrush bodies comprise an elongated rod that functions as a handle, joined to a neck, which may be generally straight or curved, which is connected to a head having a flattened section to which tufts of bristles are fastened. Such toothbrush bodies are typically manufactured in one step by injection molding; wherein, a molten thermoplastic material is injected under high pressure into a steel mold. After the plastic solidifies, the mold is opened and the fully formed toothbrush body is removed. Such a conventional toothbrush body, formed of one material, lacks the desired different coloration and physical characteristics possible with toothbrush bodies having heads and bodies manufactured of different materials. For example, it is desirable to have a rigid handle for manipulating the toothbrush with a more flexible, i.e. less rigid, head that will flex and so tend to reduce the gingival trauma associated with excess brushing pressure by the user.
U.S. Pat. No. 2,445,657, discloses toothbrush bodies having heads of a resilient material, such as vulcanized rubber, secured to rigid handles. These toothbrush bodies are manufactured in a multi-step process, wherein the heads and handles are separately produced and subsequently cemented together. Such cementing, or in general adhesive bonding, takes significant surface preparation to provide an adequate/strong seal and takes a significant time interval for the adhesive to cure or otherwise set, adversely effecting the economics of mass production.
U.S. Pat. No. 5,121,520, discloses a toothbrush having twin side-by-side brushing heads attached to the toothbrush handle at a predetermined angle. The heads may be joined to the handle by gluing, i.e. adhesive bonding, or fusion, i.e. heating the head/handle joint surfaces to a softened thermoplastic state, bringing them into intimate contact and maintaining that contact to form a joining upon cooling. Fusion, unlike gluing, requires no surface preparation and no long set-up time; however, with fusion unless there is precise heating of both the head/handle joint surfaces, it is possible to experience degradation of the plastic toothbrush material, excessive softening and distortion of the plastic, as well as, excessive flash.
There is a need in the toothbrush manufacturing art for a means of bonding pre-formed toothbrush heads to handles of different materials, having different physical properties and/or coloration, in a time interval acceptable for mass production thereof and without any degradation, distortion, excessive flash, or other consumer unacceptable effect.